PD-NOMA Technique for Out-Door FSO-OCDMA Under Various Atmospheric Conditions

Free Space Optics (FSO) technologies are gaining recognition as promising solutions to handle the increasing bandwidth demand while ensuring a high level of security. FSO systems, which utilize directional lasers and operate within a Line-of-Sight (LOS), provide information security on par with optical fiber systems. Moreover, FSO systems offer a cost-effective alternative derived from mature fiber optic telecommunications technology, making them an appealing option for resolving last mile challenges in urban telecommunications. To enhance accessibility for a larger user base, Non-Orthogonal Multiple Access (NOMA) techniques can be considered for implementation on FSO systems. Unlike Orthogonal Multiple Access (OMA) techniques, NOMA techniques allow a less complex design of telecommunications systems while maintaining high transmission rates despite a lower Signal-to-Noise Ratio (SNR). However, this decrease is unsuitable for FSO systems since they already experience low SNR, mainly due to atmospheric scintillation. Hence, exploring the integration of both OMA and NOMA techniques becomes intriguing, as it holds the potential to create a simplified FSO telecommunications system while simultaneously increasing the user capacity and transmission rate. In this study, we investigate the effectiveness of applying PD-NOMA technique to a 1x2 FSO-OCDMA transmission link affected by scintillation and atmospheric attenuation. Monte-Carlo simulations were conducted to calculate the Bit Error Rate (BER) under various atmospheric conditions. The results indicate that a 1x2 FSO-PD-NOMA transmission link can maintain reliability up to moderate atmospheric scintillation levels which could potentially double the number of users of an FSO-OCDMA telecommunication system. However, this transmission link becomes unsustainable under strong atmospheric scintillation conditions unless a tradeoff is made by decreasing the transmission rate.